The invention relates to dialkyne compounds of the formula I 
in which
R1 and R2, independently of one another, are H, F, or an alkyl radical having 1-15 carbon atoms which is unsubstituted or at least monosubstituted by halogen or CN and in which, in addition, one or more CH2 groups may each, independently of one another, be replaced by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, 
xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94 in such a way that heteroatoms are not connected directly,
X1, X2, X3 and X4 are each, independently of one another, H or xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94R3, where at least one of the groups X1, X2, X3 and X4 is xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94R3,
R3 is H, Cl, CN, SF5, CF3, or an alkyl radical having 1-15 carbon atoms which is unsubstituted or at least monosubstituted by halogen and in which, in addition, one or more CH2 groups may be replaced, in each case independently of one another, by xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Oxe2x80x94 in such a way that xe2x80x94Oxe2x80x94 atoms are not connected directly,
Q is xe2x80x94CH2xe2x80x94 or xe2x80x94Oxe2x80x94, and
Y1 and Y2, independently of one another, are C or Si,
A1 and A2, independently of one another, are a trans-1,4-cyclohexylene radical which is unsubstituted or substituted by F or CN and in which, in addition, one or more non-adjacent CH2 groups may be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94, or are 
Z1 and Z2 are each, independently of one another, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or a single bond, and
n and m, independently of one another, are 0, 1, 2 or 3, where
m+n is 1, 2 or 3.
The invention also relates to the use of the compounds of the formula I as components of liquid-crystalline media, and to liquid-crystal and electro-optical display elements which contain the liquid-crystalline media according to the invention.
The compounds of the formula I frequently have a low positive or negative value of the dielectric anisotropy and can be used as components of liquid-crystalline media, in particular for displays based on the principle of the twisted cell, the guest-host effect, the effect of deformation of aligned phases DAP or ECB (electrically controlled birefringence) or the effect of dynamic scattering.
The substances employed hitherto for this purpose all have certain disadvantages, for example inadequate stability to the action of heat, light or electric fields, or unfavorable elastic and/or dielectric properties.
The invention has an object of finding novel stable liquid-crystalline or mesogenic compounds having particularly low optical anisotropy (xcex94n) and negative or positive dielectric anisotropy (xcex94xcex5) which are suitable as components of liquid-crystalline media, in particular for TFT and STN displays.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
It has now been found that the compounds of the formula I are eminently suitable as components of liquid-crystalline media. With their aid, it is possible to obtain stable liquid-crystalline media, in particular suitable for TFT or STN displays. The novel compounds are distinguished, in particular, by high thermal stability, which is advantageous for a high holding ratio, and exhibit favorable clearing point values. At a reduced temperature of 0.9 and a wavelength of 589 nm, the compounds of the formula I have an optical anisotropy value xcex94n of  less than 0.03, preferably  less than 0.02, which is attributable to a particularly large value of n1. The reduced temperature here is defined as follows:             measurement      ⁢              xe2x80x83            ⁢      temperature      ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      K              clearing      ⁢              xe2x80x83            ⁢      point      ⁢              xe2x80x83            ⁢      temperature      ⁢              xe2x80x83            ⁢      in      ⁢              xe2x80x83            ⁢      K        =      reduced    ⁢          xe2x80x83        ⁢    temperature  
Liquid-crystalline media having very low optical anisotropy values are of particular importance for reflective and transflective applications, i.e. applications in which the respective LCD experiences no or only supporting background illumination. Low values of An are achieved by the use of substituents X1, X2, X3 and/or X4 having the highest possible polarizability. Owing to the small volume of the groups X1, X2, X3 and X4, the other LC properties, such as clearing point and viscosity, of liquid-crystalline mixtures to which the compounds according to the invention have been added are only impaired to a relatively small extent.
Very generally, the provision of compounds of the formula I considerably broadens the range of liquid-crystalline substances which are suitable, from various applicational points of view, for the preparation of liquid-crystalline mixtures.
The compounds of the formula I have a broad range of applications. Depending on the choice of substituents, these compounds can serve as base materials of which liquid-crystalline media are predominantly composed; however, it is also possible to add compounds of the formula I to liquid-crystalline base materials from other classes of compound in order, for example, to modify the dielectric and/or optical anisotropy of a dielectric of this type and/or to optimise its threshold voltage and/or its viscosity. Addition of compounds of the formula I to liquid-crystalline dielectrics enables xcex94n values of such media to be significantly reduced.
The meaning of the formula I includes all isotopes of the chemical elements bound in the compounds of the formula I. In enantiomerically pure or enriched form, the compounds of the formula I are also suitable as chiral dopants and in general for achieving chiral mesophases.
In the pure state, the compounds of the formula I are colorless and form liquid-crystalline mesophases in a temperature range which is favorably located for electro-optical use. They are stable chemically, thermally and to light.
The invention thus relates to the compounds of the formula I and to the use of these compounds as components of liquid-crystalline media. The invention furthermore relates to liquid-crystalline media comprising at least one compound of the formula I and to liquid-crystal display elements, in particular electro-optical display elements, which contain media of this type.
Above and below, n, m, R1, R2, R3, X1, X2, X3, X4, Z1, Z2, A1, A2, Q, Y1 and Y2 are as defined above, unless expressly stated otherwise. If the radical X1 occurs more than once, it may adopt identical or different meanings. The same applies to all other groups which occur more than once.
For reasons of simplicity, Cyc below denotes a cyclohexane-1,4-diyl radical or a 1- or 4-silacyclohexane-1,4-diyl radical, Dio denotes a 1,3-dioxane-2,5-diyl radical, Dit denotes a 1,3-dithiane-2,5-diyl radical, and Boc denotes a bicyclo[2,2,2]octylene radical, where Cyc may be unsubstituted or monosubstituted or polysubstituted by F or CN.
W denotes the following structural unit: 
in which X1, X2, X3, X4, Q, Y1, Y2 and Z2 are as defined above, and p is 0, 1, 2 or 3.
Preferred meanings of the group W are represented by the sub-formulae W1 to W7:
in which Z2 and R3 are as defined above.
Formula I covers the preferred compounds of the sub-formulae Ia1 to Ia12, which, besides the group W, contain a six-membered ring:
furthermore the likewise preferred compounds of the sub-formulae Ib1 to 1b72, which, in addition to the group W, contain two six-membered rings:
and the preferred compounds of the sub-formulae 1c1 to 1c55, which, besides the group W, contain three six-membered rings:
in which R1, R2, Cyc, Dio and W are as defined above.
Preference is given to compounds of the formula I which contain no isolated or aromatic C, C double bonds.
R1 and R2 are preferably, independently of one another, F, OCF3, CF3, straight-chain alkyl or alkoxy having 1 to 15 carbon atoms, in particular alkyl, alkenyl, alkenyloxy or alkoxy having up to 7 carbon atoms. In particular, preferably only one of the radicals R1 and R2 is a straight-chain alkenyl, alkoxy, alkenyl or alkenyloxy radical having up to 7 carbon atoms.
In preferred compounds of the formula I, X1, X2, X3 and/or X4 are xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94H, xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94alkyl, xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94Cl or xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94CN, where alkyl is an alkyl radical having to 1 to 15 carbon atoms. In particular, the alkyl radical is branched and is preferably tert-butyl.
In particularly preferred compounds of the formula I, X3 and X4 are simultaneously H.
Preference is furthermore given to compounds of the formula I in which only one of the groups X1, X2, X3 and X4 is not H.
xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94R3 is preferably xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94C(alkyl*)3, xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94C(alkyl*)(alkyl**)2 or xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94CH(alkyl*)2, in particular xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94C(CH3)3, xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94CH(CH3)2 or xe2x80x94Cxe2x89xa1Cxe2x80x94Cxe2x89xa1Cxe2x80x94C(CH3)2C3H7. alkyl* and alkyl** are each, independently of one another, CH3, C2H5 or C3H7.
A1 and/or A2 are preferably Cyc or Dio.
Preference is also given to compounds of the formula I and of all sub-formulae in which A1 and/or A2 is cyclohexane-1,4-diyl which is mono-substituted or disubstituted by F or CN.
A1 and/or A2 is preferably 
m and n are preferably 0, 1 or 2, in particular 0 or 1. m+n is preferably 1 or 2.
Z1 and Z2 are preferably, independently of one another, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or a single bond, particularly preferably a single bond or xe2x80x94CH2xe2x80x94CH2xe2x80x94.
Preference is given to compounds of the formula I in which R1 and R2 are simultaneously alkyl or alkoxy having 1 to 10 carbon atoms.
Preference is furthermore given to compounds of the formula I in which Y1 and Y2 are a carbon atom. Compounds of the formula I which contain not more than one dioxane ring likewise represent a preferred embodiment of the invention.
Particular preference is furthermore given to the compounds of the formulae I1 to I21 from the following group: 
in which R1, R2, R3, Z1, and Z2 are as defined above.
If R1 and/or R2 in the formulae above and below are an alkyl radical, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6 or 7 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl or heptyl, furthermore methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl or pentadecyl.
If R1 and/or R2 is an alkyl radical in which one CH2 group has been replaced by xe2x80x94Oxe2x80x94, this may be straight-chain or branched. It is preferably straight-chain and has 1 to 10 carbon atoms. The first CH2 group in this alkyl radical has preferably been replaced by xe2x80x94Oxe2x80x94, so that the radical R1 attains the meaning alkoxy and is preferably methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy or nonyloxy.
It is furthermore also possible for a CH2 group elsewhere to have been replaced by xe2x80x94Oxe2x80x94, so that the radical R1 and/or R2 is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.
If R1 and/or R2 is an alkenyl radical, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Accordingly, it is in particular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, or dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.
R1 and/or R2 is particularly preferably an alkenyl radical from the following group: 
If R1 and/or R2 is an alkenyloxy radical, this may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. It is particularly preferably a radical from the following group: 
If R1 and/or R2 is an alkyl radical in which one CH2 group has been replaced by xe2x80x94Oxe2x80x94 and one has been replaced by xe2x80x94COxe2x80x94, these are preferably adjacent. These thus contain an acyloxy group xe2x80x94COxe2x80x94Oxe2x80x94 or an oxycarbonyl group xe2x80x94Oxe2x80x94COxe2x80x94. These are preferably straight-chain and have 2 to 6 carbon atoms.
Accordingly, they are in particular acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.
If R1 and/or R2 is an alkyl radical which is at least monosubstituted by halogen, this radical is preferably straight-chain. Halogen is preferably F or Cl. In the case of polysubstitution, halogen is preferably F. The resultant radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent may be in any desired position, but is preferably in the xcfx89-position.
Compounds of the formula I having a branched wing group R1 and/or R2 may occasionally be of importance owing to better solubility in the conventional liquid-crystalline base materials, but in particular as chiral dopants if they are optically active. Smectic compounds of this type are suitable as components of ferroelectric materials.
Branched groups of this type generally contain not more than one chain branch. Preferred branched radicals R1 and/or R2 are isopropyl, 2-butyl (=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentyloxy, 3-methylpentyloxy, 2-ethylhexyloxy, 1-methylhexyloxy or 1-methylheptyloxy.
Formula I covers both the racemates of these compounds and the optical antipodes, and mixtures thereof.
Of these compounds of the formula I and the sub-formulae, preference is given to those in which at least one of the radicals present therein has one of the preferred meanings indicated.
Some very particularly preferred smaller groups of compounds of the formula I are those of the sub-formulae I22 to I36:
The compounds of the formula I are prepared by methods known per se, as described in the literature (for example in the standard works, such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for the said reactions.
Use can be made here of variants which are known per se, but are not mentioned in greater detail here.
If desired, the starting materials can also be formed in situ by not isolating them from the reaction mixture, but instead immediately converting them further into the compounds of the formula I.
The synthesis of the compounds of the formula I in which A1 and/or A2 is axially fluorinated cyclohexane can be effected by using hydrogen fluoride under pressure or by means of amine/hydrogen fluoride adducts (for example A. V. Grosse, C. B. Linn, J. Org. Chem. 3, (1938) 26; G. A. Olah, M. Nojima, I. Kerekes, Synthesis, (1973) 779); G. A. Olah, X-Y. Li, Q. Wang, G. K. S. Prakash, Synthesis (1993) 693).
The compounds according to the invention can be prepared, for example, in accordance with the following reaction schemes: 
Esters of the formula I can also be obtained by esterification of corresponding carboxylic acids (or reactive derivatives thereof) using alcohols or phenols (or reactive derivatives thereof) or by the DCC method (DCC=dicyclohexylcarbodiimide).
The corresponding carboxylic acids and alcohols are known or can be prepared analogously to known processes.
Suitable reactive derivatives of the said carboxylic acids are in particular the acid halides, especially the chlorides and bromides, furthermore the anhydrides, azides or esters, in particular alkyl esters having 1-4 carbon atoms in the alkyl group.
Suitable reactive derivatives of the said alcohols are, in particular, the corresponding metal alkoxides, preferably of an alkali metal, such as Na or K.
The esterification is advantageously carried out in the presence of an inert solvent. Highly suitable solvents are, in particular, ethers, such as diethyl ether, di-n-butyl ether, THF, dioxane and anisole, ketones, such as acetone, butanone or cyclohexanone, amides, such as DMF or hexamethylphosphoric triamide, hydrocarbons, such as benzene, toluene or xylene, halogenated hydrocarbons, such as tetrachloromethane or tetrachloroethylene, and sulfoxides, such as dimethyl sulfoxide or sulfolane. Water-immiscible solvents may advantageously be used at the same time for azeotropic removal by distillation of the water formed during the esterification. An excess of an organic base, for example pyridine, quinoline or triethylamine, may occasionally also be used as solvent for the esterification. The esterification may also be carried out in the absence of a solvent, for example by simple heating of the components in the presence of sodium acetate. The reaction temperature is usually between xe2x88x9250xc2x0 C. and +250xc2x0 C., preferably between xe2x88x9220xc2x0 C. and +80xc2x0 C. At these temperatures, the esterification reactions are generally complete after from 15 minutes to 48 hours.
In detail, the reaction conditions for the esterification depend substantially on the nature of the starting materials used. Thus, a free carboxylic acid is generally reacted with a free alcohol in the presence of a strong acid, for example a mineral acid, such as hydrochloric acid or sulfuric acid. A preferred reaction procedure is the reaction of an acid anhydride or in particular an acid chloride with an alcohol, preferably in a basic medium, important bases being, in particular, alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal carbonates or hydrogencarbonates, such as sodium carbonate, sodium hydrogencarbonate, potassium carbonate or potassium hydrogencarbonate, alkali metal acetates, such as sodium acetate or potassium acetate, alkaline earth metal hydroxides, such as calcium hydroxide, or organic bases, such as triethylamine, pyridine, lutidine, collidine or quinoline. A further preferred embodiment of the esterification comprises firstly converting the alcohol into the sodium alkoxide or potassium alkoxide, for example by treatment with ethanolic sodium hydroxide solution or potassium hydroxide solution, isolating this alkoxide, and reacting it with an acid anhydride or in particular an acid chloride.
Nitriles can be obtained by replacement of halogens using copper cyanide or alkali metal cyanide.
Ethers of the formula I are obtainable by etherification of corresponding hydroxyl compounds, the hydroxyl compound advantageously firstly being converted into a corresponding metal derivative, for example into the corresponding alkali metal alkoxide by treatment with NaH, NaNH2, NaOH, KOH, Na2CO3 or K2CO3. This alkali metal alkoxide can then be reacted with the corresponding alkyl halide, alkyl sulfonate or dialkyl sulfate, advantageously in an inert solvent, such as, for example, acetone, 1,2-dimethoxyethane, DMF or dimethyl sulfoxide, or also with an excess of aqueous or aqueous-alcoholic NaOH or KOH, at temperatures between about 20xc2x0 C. and 100xc2x0 C.
The organometallic compounds are prepared, for example, by metal-halogen exchange (for example in accordance with Org. React. 6, 339-366 (1951)) between the corresponding halogen compound and an organolithium compound, such as, preferably, tert-butyllithium or lithium naphthalenide, or by reaction with magnesium turnings.
In addition, the compounds of the formula I can be prepared by reducing a compound which conforms to the formula I, but contains one or more reducible groups and/or Cxe2x80x94C bonds in place of H atoms.
Suitable reducible groups are preferably carbonyl groups, in particular keto groups, furthermore, for example, free or esterified hydroxyl groups or aromatically bound halogen atoms. Preferred starting materials for the reduction are compounds conforming to the formula I, but which contain a cyclohexene ring or cyclohexanone ring instead of a cyclohexane ring and/or contain a xe2x80x94CH2CH2xe2x80x94 group instead of a xe2x80x94CHxe2x95x90CHxe2x80x94 group and/or contain a xe2x80x94COxe2x80x94 group instead of a xe2x80x94CH2xe2x80x94 group and/or contain a free or functionally (for example in the form of its p-toluenesulfonate) modified OH group instead of an H atom.
The reduction can be carried out, for example, by catalytic hydrogenation at temperatures between about 0xc2x0 C. and about 200xc2x0 C. and pressures between about 1 and 200 bar in an inert solvent, for example an alcohol, such as methanol, ethanol or isopropanol, an ether, such as tetrahydrofuran (THF) or dioxane, an ester, such as ethyl acetate, a carboxylic acid, such as acetic acid, or a hydrocarbon, such as cyclohexane. Suitable catalysts are advantageously noble metals, such as Pt or Pd, which can be employed in the form of oxides (for example PtO2 or PdO), on a support (for example Pd on carbon, calcium carbonate or strontium carbonate) or in finely divided form.
Ketones can also be reduced to the corresponding compounds of the formula I containing alkyl groups and/or xe2x80x94CH2CH2xe2x80x94 bridges by the methods of Clemmensen (using zinc, zinc amalgam or tin and hydrochloric acid, advantageously in aqueous-alcoholic solution or in the heterogeneous phase with water/toluene at temperatures between about 80 and 120xc2x0 C.) or Wolff-Kishner (using hydrazine, advantageously in the presence of alkali, such as KOH or NaOH, in a high-boiling solvent, such as diethylene glycol or triethylene glycol, at temperatures between about 100 and 200xc2x0 C.).
Furthermore, reductions with complex hydrides are possible. For example, arylsulfonyloxy groups can be removed reductively using LiAlH4, in particular p-toluenesulfonyloxymethyl groups can be reduced to methyl groups, advantageously in an inert solvent, such as diethyl ether or THF, at temperatures between about 0 and 100xc2x0 C.
Double bonds can be hydrogenated using NaBH4 or tributyltin hydride in methanol.
The starting materials are either known or can be prepared analogously to known compounds.
The liquid-crystalline media according to the invention preferably comprise from 2 to 40, in particular from 4 to 30, components as further constituents besides one or more compounds according to the invention. These media very particularly preferably comprise from 7 to 25 components besides one or more compounds according to the invention. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, in particular substances from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylbenzoic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarboxylic acid, cyclohexylphenyl esters of benzoic acid, of cyclohexanecarboxylic acid or of cyclohexylcyclohexanecarboxylic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclohexanes, cyclohexylcyclohexanes, cyclohexylcyclohexylcyclohexenes, 1,4-biscyclohexylbenzenes, 4,4xe2x80x2-biscyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes, 1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans, naphthalenes, decalins and substituted cinnamic acids. The 1,4-phenylene groups in these compounds may also be fluorinated.
The most important compounds suitable as further constituents of media according to the invention can be characterised by the formulae 1, 2, 3, 4 and 5:
In the formulae 1, 2, 3, 4 and 5, L and E, which may be identical or different, are each, independently of one another, a divalent radical from the group formed by -Phe-, -Cyc-, -Phexe2x80x94Phe-, -Phe-Cyc-, -Cycxe2x80x94Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and their mirror images, where Phe is unsubstituted or fluorine-substituted 1,4-phenylene, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl, and G is 2-(trans-1,4-cyclohexyl)ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
One of the radicals L and E is preferably Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. The media according to the invention preferably comprise one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which L and E are selected from the group consisting of Cyc, Phe and Pyr and simultaneously one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr and the other radical is selected from the group consisting of -Phexe2x80x94Phe-, -Phe-Cyc-, -Cycxe2x80x94Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulae 1, 2, 3, 4 and 5 in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cycxe2x80x94Cyc-, -G-Phe- and -G-Cyc-.
In a smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x2 and Rxe2x80x3 are each, independently of one another, alkyl, alkenyl, alkoxy, alkoxyalkyl, alkenyloxy or alkanoyloxy having up to 8 carbon atoms. This smaller sub-group is called group A below, and the compounds are referred to by the sub-formulae 1a, 2a, 3a, 4a and 5a. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 are different from one another, one of these radicals usually being alkyl, alkenyl, alkoxy, alkenyloxy or alkoxyalkyl.
In another smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, which is known as group B, Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS or xe2x80x94(O)iCH3-(k+I)FkClI, where i is 0 or 1, and k and I are 1, 2 or 3; the compounds in which Rxe2x80x3 has this meaning are referred to by the sub-formulae 1b, 2b, 3b, 4b and 5b. Particular preference is given to those compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b in which Rxe2x80x3 is xe2x80x94F, xe2x80x94Cl, xe2x80x94NCS, xe2x80x94CF3, xe2x80x94OCHF2 or xe2x80x94OCF3.
In the compounds of the sub-formulae 1b, 2b, 3b, 4b and 5b, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkenyl, alkoxy, alkenyloxy or alkoxyalkyl.
In a further smaller sub-group of the compounds of the formulae 1, 2, 3, 4 and 5, Rxe2x80x3 is xe2x80x94CN; this sub-group is referred to below as group C, and the compounds of this sub-group are correspondingly described by sub-formulae 1c, 2c, 3c, 4c and 5c. In the compounds of the sub-formulae 1c, 2c, 3c, 4c and 5c, Rxe2x80x2 is as defined for the compounds of the sub-formulae 1a-5a and is preferably alkyl, alkoxy or alkenyl.
Besides the preferred compounds of groups A, B and C, other compounds of the formulae 1, 2, 3, 4 and 5 having other variants of the proposed substituents are also customary. All these substances are obtainable by methods which are known from the literature or analogously thereto.
Besides the compounds of the formula I according to the invention, the media according to the invention preferably comprise one or more compounds selected from group A and/or group B and/or group C. The proportions by weight of the compounds from these groups in the media according to the invention are preferably
the sum of the proportions by weight of the group A and/or B and/or C compounds present in the respective media according to the invention preferably being 5 to 90% and in particular from 10% to 90%.
The media according to the invention preferably comprise from 1 to 40%, particularly preferably from 5 to 30%, of the compounds according to the invention. Preference is furthermore given to media comprising more than 40%, in particular from 45 to 90%, of compounds according to the invention. The media preferably comprise one or two, furthermore three to four compounds according to the invention.
The media according to the invention are prepared in a manner which is conventional per se. In general, the components are dissolved in one another, advantageously at elevated temperature. By means of suitable additives, the liquid-crystalline phases according to the invention can be modified in such a way that they can be used in all types of liquid-crystal display elements that have been disclosed hitherto. Additives of this type are known to the person skilled in the art and are described in detail in the literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example, pleochroic dyes can be added for the preparation of colored guest-host systems or substances can be added to modify the dielectric anisotropy, the viscosity and/or alignment of the nematic phases.
The entire disclosure of all applications, patents and publications, cited above and of corresponding German application No. 10035651.6, filed Jul. 20, 2000 is hereby incorporated by reference.